1. Field of the Invention
This invention relates generally to induction coils, and is more particularly concerned with a wire core for induction coils such as transformers, chokes and the like.
2. Discussion of the Prior Art
It is common for transformers and other induction devices to be made up of a core comprising a plurality of sheets of steel, the sheets being die cut and stacked to create the desired thickness of a core. The individual sheets are varnished or otherwise electrically insulated from one another in order to reduce eddy currents in the core, and the thickness of the individual sheets is selected to minimize eddy currents.
The core of a transformer or the like generally passes through the center of the electric winding, and closes on itself to provide a closed magnetic circuit. Since the core then supports the electric winding, it is natural that the core has been used as the support for the transformer. That is to say, one attaches the core to a container or baseboard in order to support the transformer.
Transformers and other induction coils inherently generate heat, and the heat must be dissipated or the power characteristics of the device will change. If the device becomes too hot, the electric winding can become short circuited and burn out the coil. In small devices, one usually relies on air cooling, sometimes with metal fins or the like to assist in dissipating the heat. In larger devices, the coils and core may be immersed in oil. One then may use fins on the container, radiator pipes, or both, so convection currents move the heated oil through the cooling fins or pipes. If further cooling is needed, one generally resorts to fans to move more air across the cooling means.
When a stack of metal sheets is used as the core for an induction coil, it is usual to provide a shape, such as an E with the electric winding on the center leg of the E. After the coil is in place, in additional stack of sheets is applied to connect the ends of the E, thereby completing the magnetic circuit. Using such a technique, it will be understood that the coil is necessarily wound separately, and subsequently placed on the core. The coil must therefore be big enough to slip onto the core. Such construction contributes to the inherent noisiness of an induction coil, because the electric winding must be somewhat loose on the core. As a result, when an alternating voltage is applied to the electric winding, the sheets making up the core tend to vibrate with the alternating magnetic field. Any gaps and spaces between the electrical components and the magnetic components reduce coupling and efficiency of action.